From what I've read, the APS knots are manufactured by the well known Chinese manufacturers but to a better standard specified by APS.
That's correct. I have enough specimens to show and prove this. Upon request, Andrew @APShave can provide the same information to justify the case. The general perception is there are limited number of manufacturers, all in China, and they are the same. Let me assure you they are not. If you put 5 APS (different knots, different sizes) vs same Yaqies the difference can be seen and felt, much greater when they are lathered and used.
I agree Muhle/EJ brushes can develop "doughnut" shape/effect. But I'll not consider them a good example or use them for comparison. First, they stopped their advancement in synthetic fiber technology at the level of "Silvertip Fibre" and second, more important, their biggest size is 25mm/XL, not very dense. Again, the argument goes only for much larger sizes,
28mm and
30mm with shorter lofts. This combination makes a day and night difference, imo. They don't develop “doughnut", black hole or any other shape rather their original/natural one only.
To summarize again the main the advantages of bigger size knots at lower loft, in synthetics!: increased backbone/stiffness, less flop (spill of water or lather), smaller bloom/bulb (visually no more than 26mm, makes them not so huge and more aesthetically appealing) and better/faster lathering, particularly with hard soaps (more economical also). There are many other smaller details and improvements not worth mentioning, but contributing as well. At this moment I can't see any disadvantages, but like we say, YMMV.
A picture is worth a thousand words and if I find a time to make some, side and top views, they will show the big, big difference between 30mm Yaqi, 25mm/XL Muhle/EJ vs 30mm APS Cashmere and 30mm APS SynBad at lower lofts (set at custom wood handles). For example, my 30mm APS is shorter, more dense, with better backbone and softer tips and with smaller bulb/bloom at the top vs. 25mm Muhle/EJ. It is the closest thing visually and in performance to natural, maybe 2-band badger. At the same time original 30mm Yaqi barberpole handle is huge, floppy and leaking - probably appropriate only for dome shave. I've been setting knots and making brushes for the last 2 years and I played with most knots from various manufacturers, experimenting with lofts at every length and handle's hole sizes to collect enough data and get the results I wanted. What pictures can't show is the difference in shave in real life. You may have to take my word on it ... or not